[DOCS] Add connector incident settings to Cases #311
Description
This PR allows users to specify connector incident fields when cases are being sent to them. Specifically:
Jira: issue type, priority, and parent issue in the case of a subtask.
IBM Resilient: issue types, and severity.
ServiceNow: urgency, severity, and impact.
Ref: elastic/kibana#76222, elastic/kibana#76212, elastic/kibana#75622